Method and apparatus for transmitting information in wireless communication system

ABSTRACT

A method and apparatus for transmitting information in a wireless communication system is provided. A first node receives an indication which indicates that a secondary cell (SCell) is added by a user equipment (UE), and information on the added SCell, and transmits an SCell addition request, including the information on the added SCell and an identity of the UE, to a second node. Alternatively, a method for transmitting information in a wireless communication system is provided. The first node receives an indication which indicates that an SCell is released by a UE, and information on the released SCell, and transmits an SCell release request, including the information on the released SCell and an identity of the UE, to a second node.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to wireless communications, and morespecifically, to a method and apparatus for transmitting information ina wireless communication system.

2. Related Art

Universal mobile telecommunications system (UMTS) is a 3^(rd) generation(3G) asynchronous mobile communication system operating in wideband codedivision multiple access (WCDMA) based on European systems, globalsystem for mobile communications (GSM) and general packet radio services(GPRS). A long-term evolution (LTE) of UMTS is under discussion by the3^(rd) generation partnership project (3GPP) that standardized UMTS.

The 3GPP LTE is a technology for enabling high-speed packetcommunications. Many schemes have been proposed for the LTE objectiveincluding those that aim to reduce user and provider costs, improveservice quality, and expand and improve coverage and system capacity.The 3GPP LTE requires reduced cost per bit, increased serviceavailability, flexible use of a frequency band, a simple structure, anopen interface, and adequate power consumption of a terminal as anupper-level requirement.

Small cells using low power nodes are considered promising to cope withmobile traffic explosion, especially for hotspot deployments in indoorand outdoor scenarios. A low-power node generally means a node whosetransmission (Tx) power is lower than macro node and base station (BS)classes, for example a pico and femto eNodeB (eNB) are both applicable.Small cell enhancements for 3GPP LTE will focus on additionalfunctionalities for enhanced performance in hotspot areas for indoor andoutdoor using low power nodes.

Some of activities will focus on achieving an even higher degree ofinterworking between the macro and low-power layers, including differentforms of macro assistance to the low-power layer and dual-layerconnectivity. Dual connectivity implies that the device has simultaneousconnections to both macro and low-power layers. Macro assistanceincluding dual connectivity may provide several benefits:

-   -   —Enhanced support for mobility—by maintaining the mobility        anchor point in the macro layer, it is possible to maintain        seamless mobility between macro and low-power layers, as well as        between low-power nodes.    -   Low overhead transmissions from the low-power layer—by        transmitting only information required for individual user        experience, it is possible to avoid overhead coming from        supporting idle-mode mobility within the local-area layer, for        example.    -   Energy-efficient load balancing—by turning off the low-power        nodes when there is no ongoing data transmission, it is possible        to reduce the energy consumption of the low-power layer.    -   Per-link optimization—by being able to select the termination        point for uplink and downlink separately, the node selection can        be optimized for each link.

Carrier aggregation (CA) may be introduced. In CA, two or more componentcarriers (CCs) are aggregated in order to support wider transmissionbandwidths up to 100 MHz. A UE may simultaneously receive or transmit onone or multiple CCs depending on its capabilities. A Rel-10 UE withreception and/or transmission capabilities for CA can simultaneouslyreceive and/or transmit on multiple CCs corresponding to multipleserving cells. A Rel-8/9 UE can receive on a single CC and transmit on asingle CC corresponding to one serving cell only.

When CA is configured, a user equipment (UE) only has one radio resourcecontrol (RRC) connection with the network. At RRC connectionestablishment/re-establishment/handover, one serving cell provides thenon-access stratum (NAS) mobility information (e.g., tracking areaidentity (TAI)), and at RRC connection re-establishment/handover, oneserving cell provides the security input. This cell is referred to asthe primary cell (PCell). In the downlink, the carrier corresponding tothe PCell is the downlink primary component carrier (DL PCC) while inthe uplink it is the uplink primary component carrier (UL PCC).

Depending on UE capabilities, secondary cells (SCells) can be configuredto form together with the PCell a set of serving cells. In the downlink,the carrier corresponding to an SCell is a downlink secondary componentcarrier (DL SCC) while in the uplink it is an uplink secondary componentcarrier (UL SCC).

When the UE reports measurement results about one or more cells on oneor more frequencies to the eNB, the eNB could send RRC connectionreconfiguration to the UE in order to configure one or more SCells. Uponreceiving the RRC connection reconfiguration including SCellconfigurations, the UE configures one or more SCells. Hence, the UEconfigures the SCell under the network's control.

A method for configuring the SCell more efficiently may be required.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus for transmittinginformation in a wireless communication system. The present inventionprovides a method for transmitting an SCell addition/release request,including the information on the added/released SCell and an identity ofa UE.

In an aspect, a method for transmitting, by a first node, information ina wireless communication system is provided. The method includesreceiving an indication which indicates that a secondary cell (SCell) isadded by a user equipment (UE), and information on the added SCell, andtransmitting an SCell addition request, including the information on theadded SCell and an identity of the UE, to a second node.

The information on the added SCell may include at least one of an indexof the added SCell, a frequency of the added SCell, and a cellidentifier (ID) of the added SCell.

The index of the added SCell may be an index not assigned to otherconfigured SCell.

The indication and the information on the added SCell may be receivedvia a small cell indication message.

The first node may be a master eNodeB (MeNB) controlling a primary cell(PCell), and the second node may be a secondary eNodeB (SeNB)controlling the SCell.

The first node and the second node may be different from each other.

The method may further include receiving an SCell addition response fromthe second node as a response to the SCell addition request.

In another aspect, a method for transmitting, by a first node,information in a wireless communication system is provided. The methodincludes receiving an indication which indicates that a secondary cell(SCell) is released by a user equipment (UE), and information on thereleased SCell, and transmitting an SCell release request, including theinformation on the released SCell and an identity of the UE, to a secondnode.

The information on the released SCell may include an index of thereleased SCell.

The indication and the information on the released SCell may be receivedvia a small cell indication message.

The method may further include receiving an SCell release response fromthe second node as a response to the SCell release request.

In another aspect, a method for adding, by a user equipment (UE), asecondary cell (SCell) in a wireless communication system is provided.The method include receiving a list of potential SCells, an SCellconfiguration, and a condition of SCell addition, measuring one or moreSCells, adding an SCell if the SCell meets the condition of SCelladdition and if the SCell is included in the list of potential SCells,and transmitting an index of the added SCell to an eNodeB (eNB).

The index of the added SCell may be an index not assigned to otherconfigured SCells.

SCell addition/release can be informed to a second node from a firstnode, when the first node controlling a PCell and the second nodecontrolling the SCell is different from each other.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows LTE system architecture.

FIG. 2 shows a control plane of a radio interface protocol of an LTEsystem.

FIG. 3 shows a user plane of a radio interface protocol of an LTEsystem.

FIG. 4 shows an example of a physical channel structure.

FIG. 5 shows deployment scenarios of small cells with/without macrocoverage.

FIGS. 6 and 7 show an intra-MME/S-GW handover procedure.

FIG. 8 shows a scenario of dual connectivity.

FIG. 9 shows a UE-based SCell addition procedure according to anembodiment of the present invention.

FIG. 10 shows a UE-based SCell release procedure according to anembodiment of the present invention.

FIG. 11 shows an example of a method for transmitting informationaccording to an embodiment of the present invention.

FIG. 12 shows an example of a method for transmitting informationaccording to another embodiment of the present invention.

FIG. 13 is a block diagram showing wireless communication system toimplement an embodiment of the present invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The technology described below can be used in various wirelesscommunication systems such as code division multiple access (CDMA),frequency division multiple access (FDMA), time division multiple access(TDMA), orthogonal frequency division multiple access (OFDMA), singlecarrier frequency division multiple access (SC-FDMA), etc. The CDMA canbe implemented with a radio technology such as universal terrestrialradio access (UTRA) or CDMA-2000. The TDMA can be implemented with aradio technology such as global system for mobile communications(GSM)/general packet ratio service (GPRS)/enhanced data rate for GSMevolution (EDGE). The OFDMA can be implemented with a radio technologysuch as institute of electrical and electronics engineers (IEEE) 802.11(Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, evolved UTRA (E-UTRA), etc.IEEE 802.16m is evolved from IEEE 802.16e, and provides backwardcompatibility with a system based on the IEEE 802.16e. The UTRA is apart of a universal mobile telecommunication system (UMTS). 3^(rd)generation partnership project (3GPP) long term evolution (LTE) is apart of an evolved UMTS (E-UMTS) using the E-UTRA. The 3GPP LTE uses theOFDMA in a downlink and uses the SC-FDMA in an uplink. LTE-advanced(LTE-A) is an evolution of the LTE.

For clarity, the following description will focus on LTE-A. However,technical features of the present invention are not limited thereto.

FIG. 1 shows LTE system architecture. The communication network iswidely deployed to provide a variety of communication services such asvoice over internet protocol (VoIP) through IMS and packet data.

Referring to FIG. 1, the LTE system architecture includes one or moreuser equipment (UE; 10), an evolved-UMTS terrestrial radio accessnetwork (E-UTRAN) and an evolved packet core (EPC). The UE 10 refers toa communication equipment carried by a user. The UE 10 may be fixed ormobile, and may be referred to as another terminology, such as a mobilestation (MS), a user terminal (UT), a subscriber station (SS), awireless device, etc.

The E-UTRAN includes one or more evolved node-B (eNB) 20, and aplurality of UEs may be located in one cell. The eNB 20 provides an endpoint of a control plane and a user plane to the UE 10. The eNB 20 isgenerally a fixed station that communicates with the UE 10 and may bereferred to as another terminology, such as a base station (BS), a basetransceiver system (BTS), an access point, etc. One eNB 20 may bedeployed per cell. There are one or more cells within the coverage ofthe eNB 20. A single cell is configured to have one of bandwidthsselected from 1.25, 2.5, 5, 10, and 20 MHz, etc., and provides downlinkor uplink transmission services to several UEs. In this case, differentcells can be configured to provide different bandwidths.

Hereinafter, a downlink (DL) denotes communication from the eNB 20 tothe UE 10, and an uplink (UL) denotes communication from the UE 10 tothe eNB 20. In the DL, a transmitter may be a part of the eNB 20, and areceiver may be a part of the UE 10. In the UL, the transmitter may be apart of the UE 10, and the receiver may be a part of the eNB 20.

The EPC includes a mobility management entity (MME) which is in chargeof control plane functions, and a system architecture evolution (SAE)gateway (S-GW) which is in charge of user plane functions. The MME/S-GW30 may be positioned at the end of the network and connected to anexternal network. The MME has UE access information or UE capabilityinformation, and such information may be primarily used in UE mobilitymanagement. The S-GW is a gateway of which an endpoint is an E-UTRAN.The MME/S-GW 30 provides an end point of a session and mobilitymanagement function for the UE 10. The EPC may further include a packetdata network (PDN) gateway (PDN-GW). The PDN-GW is a gateway of which anendpoint is a PDN.

The MME provides various functions including non-access stratum (NAS)signaling to eNBs 20, NAS signaling security, access stratum (AS)security control, Inter core network (CN) node signaling for mobilitybetween 3GPP access networks, idle mode UE reachability (includingcontrol and execution of paging retransmission), tracking area listmanagement (for UE in idle and active mode), P-GW and S-GW selection,MME selection for handovers with MME change, serving GPRS support node(SGSN) selection for handovers to 2G or 3G 3GPP access networks,roaming, authentication, bearer management functions including dedicatedbearer establishment, support for public warning system (PWS) (whichincludes earthquake and tsunami warning system (ETWS) and commercialmobile alert system (CMAS)) message transmission. The S-GW host providesassorted functions including per-user based packet filtering (by e.g.,deep packet inspection), lawful interception, UE Internet protocol (IP)address allocation, transport level packet marking in the DL, UL and DLservice level charging, gating and rate enforcement, DL rate enforcementbased on APN-AMBR. For clarity MME/S-GW 30 will be referred to hereinsimply as a “gateway,” but it is understood that this entity includesboth the MME and S-GW.

Interfaces for transmitting user traffic or control traffic may be used.The UE 10 and the eNB 20 are connected by means of a Uu interface. TheeNBs 20 are interconnected by means of an X2 interface. Neighboring eNBsmay have a meshed network structure that has the X2 interface. The eNBs20 are connected to the EPC by means of an S1 interface. The eNBs 20 areconnected to the MME by means of an S1-MME interface, and are connectedto the S-GW by means of S1-U interface. The S1 interface supports amany-to-many relation between the eNB 20 and the MME/S-GW.

The eNB 20 may perform functions of selection for gateway 30, routingtoward the gateway 30 during a radio resource control (RRC) activation,scheduling and transmitting of paging messages, scheduling andtransmitting of broadcast channel (BCH) information, dynamic allocationof resources to the UEs 10 in both UL and DL, configuration andprovisioning of eNB measurements, radio bearer control, radio admissioncontrol (RAC), and connection mobility control in LTE_ACTIVE state. Inthe EPC, and as noted above, gateway 30 may perform functions of pagingorigination, LTE_IDLE state management, ciphering of the user plane, SAEbearer control, and ciphering and integrity protection of NAS signaling.

FIG. 2 shows a control plane of a radio interface protocol of an LTEsystem. FIG. 3 shows a user plane of a radio interface protocol of anLTE system.

Layers of a radio interface protocol between the UE and the E-UTRAN maybe classified into a first layer (L1), a second layer (L2), and a thirdlayer (L3) based on the lower three layers of the open systeminterconnection (OSI) model that is well-known in the communicationsystem. The radio interface protocol between the UE and the E-UTRAN maybe horizontally divided into a physical layer, a data link layer, and anetwork layer, and may be vertically divided into a control plane(C-plane) which is a protocol stack for control signal transmission anda user plane (U-plane) which is a protocol stack for data informationtransmission. The layers of the radio interface protocol exist in pairsat the UE and the E-UTRAN, and are in charge of data transmission of theUu interface.

A physical (PHY) layer belongs to the L1. The PHY layer provides ahigher layer with an information transfer service through a physicalchannel. The PHY layer is connected to a medium access control (MAC)layer, which is a higher layer of the PHY layer, through a transportchannel. A physical channel is mapped to the transport channel. Data istransferred between the MAC layer and the PHY layer through thetransport channel. Between different PHY layers, i.e., a PHY layer of atransmitter and a PHY layer of a receiver, data is transferred throughthe physical channel using radio resources. The physical channel ismodulated using an orthogonal frequency division multiplexing (OFDM)scheme, and utilizes time and frequency as a radio resource.

The PHY layer uses several physical control channels. A physicaldownlink control channel (PDCCH) reports to a UE about resourceallocation of a paging channel (PCH) and a downlink shared channel(DL-SCH), and hybrid automatic repeat request (HARQ) information relatedto the DL-SCH. The PDCCH may carry a UL grant for reporting to the UEabout resource allocation of UL transmission. A physical control formatindicator channel (PCFICH) reports the number of OFDM symbols used forPDCCHs to the UE, and is transmitted in every subframe. A physicalhybrid ARQ indicator channel (PHICH) carries an HARQ acknowledgement(ACK)/non-acknowledgement (NACK) signal in response to UL transmission.A physical uplink control channel (PUCCH) carries UL control informationsuch as HARQ ACK/NACK for DL transmission, scheduling request, and CQI.A physical uplink shared channel (PUSCH) carries a UL-uplink sharedchannel (SCH).

FIG. 4 shows an example of a physical channel structure.

A physical channel consists of a plurality of subframes in time domainand a plurality of subcarriers in frequency domain. One subframeconsists of a plurality of symbols in the time domain. One subframeconsists of a plurality of resource blocks (RBs). One RB consists of aplurality of symbols and a plurality of subcarriers. In addition, eachsubframe may use specific subcarriers of specific symbols of acorresponding subframe for a PDCCH. For example, a first symbol of thesubframe may be used for the PDCCH. The PDCCH carries dynamic allocatedresources, such as a physical resource block (PRB) and modulation andcoding scheme (MCS). A transmission time interval (TTI) which is a unittime for data transmission may be equal to a length of one subframe. Thelength of one subframe may be 1 ms.

The transport channel is classified into a common transport channel anda dedicated transport channel according to whether the channel is sharedor not. A DL transport channel for transmitting data from the network tothe UE includes a broadcast channel (BCH) for transmitting systeminformation, a paging channel (PCH) for transmitting a paging message, aDL-SCH for transmitting user traffic or control signals, etc. The DL-SCHsupports HARQ, dynamic link adaptation by varying the modulation, codingand transmit power, and both dynamic and semi-static resourceallocation. The DL-SCH also may enable broadcast in the entire cell andthe use of beamforming. The system information carries one or moresystem information blocks. All system information blocks may betransmitted with the same periodicity. Traffic or control signals of amultimedia broadcast/multicast service (MBMS) may be transmitted throughthe DL-SCH or a multicast channel (MCH).

A UL transport channel for transmitting data from the UE to the networkincludes a random access channel (RACH) for transmitting an initialcontrol message, a UL-SCH for transmitting user traffic or controlsignals, etc. The UL-SCH supports HARQ and dynamic link adaptation byvarying the transmit power and potentially modulation and coding. TheUL-SCH also may enable the use of beamforming. The RACH is normally usedfor initial access to a cell.

A MAC layer belongs to the L2. The MAC layer provides services to aradio link control (RLC) layer, which is a higher layer of the MAClayer, via a logical channel. The MAC layer provides a function ofmapping multiple logical channels to multiple transport channels. TheMAC layer also provides a function of logical channel multiplexing bymapping multiple logical channels to a single transport channel. A MACsublayer provides data transfer services on logical channels.

The logical channels are classified into control channels fortransferring control plane information and traffic channels fortransferring user plane information, according to a type of transmittedinformation. That is, a set of logical channel types is defined fordifferent data transfer services offered by the MAC layer. The logicalchannels are located above the transport channel, and are mapped to thetransport channels.

The control channels are used for transfer of control plane informationonly. The control channels provided by the MAC layer include a broadcastcontrol channel (BCCH), a paging control channel (PCCH), a commoncontrol channel (CCCH), a multicast control channel (MCCH) and adedicated control channel (DCCH). The BCCH is a downlink channel forbroadcasting system control information. The PCCH is a downlink channelthat transfers paging information and is used when the network does notknow the location cell of a UE. The CCCH is used by UEs having no RRCconnection with the network. The MCCH is a point-to-multipoint downlinkchannel used for transmitting MBMS control information from the networkto a UE. The DCCH is a point-to-point bi-directional channel used by UEshaving an RRC connection that transmits dedicated control informationbetween a UE and the network.

Traffic channels are used for the transfer of user plane informationonly. The traffic channels provided by the MAC layer include a dedicatedtraffic channel (DTCH) and a multicast traffic channel (MTCH). The DTCHis a point-to-point channel, dedicated to one UE for the transfer ofuser information and can exist in both uplink and downlink. The MTCH isa point-to-multipoint downlink channel for transmitting traffic datafrom the network to the UE.

Uplink connections between logical channels and transport channelsinclude the DCCH that can be mapped to the UL-SCH, the DTCH that can bemapped to the UL-SCH and the CCCH that can be mapped to the UL-SCH.Downlink connections between logical channels and transport channelsinclude the BCCH that can be mapped to the BCH or DL-SCH, the PCCH thatcan be mapped to the PCH, the DCCH that can be mapped to the DL-SCH, andthe DTCH that can be mapped to the DL-SCH, the MCCH that can be mappedto the MCH, and the MTCH that can be mapped to the MCH.

An RLC layer belongs to the L2. The RLC layer provides a function ofadjusting a size of data, so as to be suitable for a lower layer totransmit the data, by concatenating and segmenting the data receivedfrom an upper layer in a radio section. In addition, to ensure a varietyof quality of service (QoS) required by a radio bearer (RB), the RLClayer provides three operation modes, i.e., a transparent mode (TM), anunacknowledged mode (UM), and an acknowledged mode (AM). The AM RLCprovides a retransmission function through an automatic repeat request(ARQ) for reliable data transmission. Meanwhile, a function of the RLClayer may be implemented with a functional block inside the MAC layer.In this case, the RLC layer may not exist.

A packet data convergence protocol (PDCP) layer belongs to the L2. ThePDCP layer provides a function of header compression function thatreduces unnecessary control information such that data being transmittedby employing IP packets, such as IPv4 or IPv6, can be efficientlytransmitted over a radio interface that has a relatively smallbandwidth. The header compression increases transmission efficiency inthe radio section by transmitting only necessary information in a headerof the data. In addition, the PDCP layer provides a function ofsecurity. The function of security includes ciphering which preventsinspection of third parties, and integrity protection which preventsdata manipulation of third parties.

A radio resource control (RRC) layer belongs to the L3. The RLC layer islocated at the lowest portion of the L3, and is only defined in thecontrol plane. The RRC layer takes a role of controlling a radioresource between the UE and the network. For this, the UE and thenetwork exchange an RRC message through the RRC layer. The RRC layercontrols logical channels, transport channels, and physical channels inrelation to the configuration, reconfiguration, and release of RBs. AnRB is a logical path provided by the L1 and L2 for data delivery betweenthe UE and the network. That is, the RB signifies a service provided theL2 for data transmission between the UE and E-UTRAN. The configurationof the RB implies a process for specifying a radio protocol layer andchannel properties to provide a particular service and for determiningrespective detailed parameters and operations. The RB is classified intotwo types, i.e., a signaling RB (SRB) and a data RB (DRB). The SRB isused as a path for transmitting an RRC message in the control plane. TheDRB is used as a path for transmitting user data in the user plane.

Referring to FIG. 2, the RLC and MAC layers (terminated in the eNB onthe network side) may perform functions such as scheduling, automaticrepeat request (ARQ), and hybrid automatic repeat request (HARQ). TheRRC layer (terminated in the eNB on the network side) may performfunctions such as broadcasting, paging, RRC connection management, RBcontrol, mobility functions, and UE measurement reporting andcontrolling. The NAS control protocol (terminated in the MME of gatewayon the network side) may perform functions such as a SAE bearermanagement, authentication, LTE_IDLE mobility handling, pagingorigination in LTE_IDLE, and security control for the signaling betweenthe gateway and UE.

Referring to FIG. 3, the RLC and MAC layers (terminated in the eNB onthe network side) may perform the same functions for the control plane.The PDCP layer (terminated in the eNB on the network side) may performthe user plane functions such as header compression, integrityprotection, and ciphering.

An RRC state indicates whether an RRC layer of the UE is logicallyconnected to an RRC layer of the E-UTRAN. The RRC state may be dividedinto two different states such as an RRC connected state and an RRC idlestate. When an RRC connection is established between the RRC layer ofthe UE and the RRC layer of the E-UTRAN, the UE is in RRC_CONNECTED, andotherwise the UE is in RRC_IDLE. Since the UE in RRC_CONNECTED has theRRC connection established with the E-UTRAN, the E-UTRAN may recognizethe existence of the UE in RRC_CONNECTED and may effectively control theUE. Meanwhile, the UE in RRC_IDLE may not be recognized by the E-UTRAN,and a CN manages the UE in unit of a TA which is a larger area than acell. That is, only the existence of the UE in RRC_IDLE is recognized inunit of a large area, and the UE must transition to RRC_CONNECTED toreceive a typical mobile communication service such as voice or datacommunication.

In RRC_IDLE state, the UE may receive broadcasts of system informationand paging information while the UE specifies a discontinuous reception(DRX) configured by NAS, and the UE has been allocated an identification(ID) which uniquely identifies the UE in a tracking area and may performpublic land mobile network (PLMN) selection and cell re-selection. Also,in RRC_IDLE state, no RRC context is stored in the eNB.

In RRC_CONNECTED state, the UE has an E-UTRAN RRC connection and acontext in the E-UTRAN, such that transmitting and/or receiving datato/from the eNB becomes possible. Also, the UE can report channelquality information and feedback information to the eNB. InRRC_CONNECTED state, the E-UTRAN knows the cell to which the UE belongs.Therefore, the network can transmit and/or receive data to/from UE, thenetwork can control mobility (handover and inter-radio accesstechnologies (RAT) cell change order to GSM EDGE radio access network(GERAN) with network assisted cell change (NACC)) of the UE, and thenetwork can perform cell measurements for a neighboring cell.

In RRC_IDLE state, the UE specifies the paging DRX cycle. Specifically,the UE monitors a paging signal at a specific paging occasion of everyUE specific paging DRX cycle. The paging occasion is a time intervalduring which a paging signal is transmitted. The UE has its own pagingoccasion.

A paging message is transmitted over all cells belonging to the sametracking area. If the UE moves from one TA to another TA, the UE willsend a tracking area update (TAU) message to the network to update itslocation.

When the user initially powers on the UE, the UE first searches for aproper cell and then remains in RRC_IDLE in the cell. When there is aneed to establish an RRC connection, the UE which remains in RRC_IDLEestablishes the RRC connection with the RRC of the E-UTRAN through anRRC connection procedure and then may transition to RRC_CONNECTED. TheUE which remains in RRC_IDLE may need to establish the RRC connectionwith the E-UTRAN when uplink data transmission is necessary due to auser's call attempt or the like or when there is a need to transmit aresponse message upon receiving a paging message from the E-UTRAN.

It is known that different cause values may be mapped o the signaturesequence used to transmit messages between a UE and eNB and that eitherchannel quality indicator (CQI) or path loss and cause or message sizeare candidates for inclusion in the initial preamble.

When a UE wishes to access the network and determines a message to betransmitted, the message may be linked to a purpose and a cause valuemay be determined. The size of the ideal message may be also bedetermined by identifying all optional information and differentalternative sizes, such as by removing optional information, or analternative scheduling request message may be used.

The UE acquires necessary information for the transmission of thepreamble, UL interference, pilot transmit power and requiredsignal-to-noise ratio (SNR) for the preamble detection at the receiveror combinations thereof. This information must allow the calculation ofthe initial transmit power of the preamble. It is beneficial to transmitthe UL message in the vicinity of the preamble from a frequency point ofview in order to ensure that the same channel is used for thetransmission of the message.

The UE should take into account the UL interference and the UL path lossin order to ensure that the network receives the preamble with a minimumSNR. The UL interference can be determined only in the eNB, andtherefore, must be broadcast by the eNB and received by the UE prior tothe transmission of the preamble. The UL path loss can be considered tobe similar to the DL path loss and can be estimated by the UE from thereceived RX signal strength when the transmit power of some pilotsequence of the cell is known to the UE.

The required UL SNR for the detection of the preamble would typicallydepend on the eNB configuration, such as a number of Rx antennas andreceiver performance. There may be advantages to transmit the ratherstatic transmit power of the pilot and the necessary UL SNR separatelyfrom the varying UL interference and possibly the power offset requiredbetween the preamble and the message.

The initial transmission power of the preamble can be roughly calculatedaccording to the following formula:

Transmit power=TransmitPilot−RxPilot+ULInterference+Offset+SNRRequired

Therefore, any combination of SNRRequired, ULInterference, TransmitPilotand Offset can be broadcast. In principle, only one value must bebroadcast. This is essentially in current UMTS systems, although the ULinterference in 3GPP LTE will mainly be neighboring cell interferencethat is probably more constant than in UMTS system.

The UE determines the initial UL transit power for the transmission ofthe preamble as explained above. The receiver in the eNB is able toestimate the absolute received power as well as the relative receivedpower compared to the interference in the cell. The eNB will consider apreamble detected if the received signal power compared to theinterference is above an eNB known threshold.

The UE performs power ramping in order to ensure that a UE can bedetected even if the initially estimated transmission power of thepreamble is not adequate. Another preamble will most likely betransmitted if no ACK or NACK is received by the UE before the nextrandom access attempt. The transmit power of the preamble can beincreased, and/or the preamble can be transmitted on a different ULfrequency in order to increase the probability of detection. Therefore,the actual transmit power of the preamble that will be detected does notnecessarily correspond to the initial transmit power of the preamble asinitially calculated by the UE.

The UE must determine the possible UL transport format. The transportformat, which may include MCS and a number of resource blocks thatshould be used by the UE, depends mainly on two parameters, specificallythe SNR at the eNB and the required size of the message to betransmitted.

In practice, a maximum UE message size, or payload, and a requiredminimum SNR correspond to each transport format. In UMTS, the UEdetermines before the transmission of the preamble whether a transportformat can be chosen for the transmission according to the estimatedinitial preamble transmit power, the required offset between preambleand the transport block, the maximum allowed or available UE transmitpower, a fixed offset and additional margin. The preamble in UMTS neednot contain any information regarding the transport format selected bythe EU since the network does not need to reserve time and frequencyresources and, therefore, the transport format is indicated togetherwith the transmitted message.

The eNB must be aware of the size of the message that the UE intends totransmit and the SNR achievable by the UE in order to select the correcttransport format upon reception of the preamble and then reserve thenecessary time and frequency resources. Therefore, the eNB cannotestimate the SNR achievable by the EU according to the received preamblebecause the UE transmit power compared to the maximum allowed orpossible UE transmit power is not known to the eNB, given that the UEwill most likely consider the measured path loss in the DL or someequivalent measure for the determination of the initial preambletransmission power.

The eNB could calculate a difference between the path loss estimated inthe DL compared and the path loss of the UL. However, this calculationis not possible if power ramping is used and the UE transmit power forthe preamble does not correspond to the initially calculated UE transmitpower. Furthermore, the precision of the actual UE transmit power andthe transmit power at which the UE is intended to transmit is very low.Therefore, it has been proposed to code the path loss or CQI estimationof the downlink and the message size or the cause value In the UL in thesignature.

FIG. 5 shows deployment scenarios of small cells with/without macrocoverage. Small cell enhancement should target both with and withoutmacro coverage, both outdoor and indoor small cell deployments and bothideal and non-ideal backhaul. Both sparse and dense small celldeployments should be considered.

Referring to FIG. 5, small cell enhancement should target the deploymentscenario in which small cell nodes are deployed under the coverage ofone or more than one overlaid E-UTRAN macro-cell layer(s) in order toboost the capacity of already deployed cellular network. Two scenarioswhere the UE is in coverage of both the macro cell and the small cellsimultaneously, and where the UE is not in coverage of both the macrocell and the small cell simultaneously can be considered. Also, thedeployment scenario where small cell nodes are not deployed under thecoverage of one or more overlaid E-UTRAN macro-cell layer(s) may beconsidered.

Small cell enhancement should target both outdoor and indoor small celldeployments. The small cell nodes could be deployed indoors or outdoors,and in either case could provide service to indoor or outdoor UEs.

Handover (HO) is described. It may be referred to Section 10.1.2.1 of3GPP TS 36.300 V11.4.0 (2012-12).

The intra E-UTRAN HO of a UE in RRC_CONNECTED state is a UE-assistednetwork-controlled HO, with HO preparation signaling in E-UTRAN:

-   -   Part of the HO command comes from the target eNB and is        transparently forwarded to the UE by the source eNB;    -   To prepare the HO, the source eNB passes all necessary        information to the target eNB (e.g., E-UTRAN radio access bearer        (E-RAB) attributes and RRC context): When carrier aggregation        (CA) is configured and to enable secondary cell (SCell)        selection in the target eNB, the source eNB can provide in        decreasing order of radio quality a list of the best cells and        optionally measurement result of the cells.    -   Both the source eNB and UE keep some context (e.g., C-RNTI) to        enable the return of the UE in case of HO failure;    -   UE accesses the target cell via RACH following a contention-free        procedure using a dedicated RACH preamble or following a        contention-based procedure if dedicated RACH preambles are not        available: the UE uses the dedicated preamble until the handover        procedure is finished (successfully or unsuccessfully);    -   If the RACH procedure towards the target cell is not successful        within a certain time, the UE initiates radio link failure        recovery using the best cell;    -   No robust header compression (ROHC) context is transferred at        handover.

First, C-plane handling is described. The preparation and executionphase of the HO procedure is performed without EPC involvement, i.e.,preparation messages are directly exchanged between the eNBs. Therelease of the resources at the source side during the HO completionphase is triggered by the eNB. In case an RN is involved, its donor eNB(DeNB) relays the appropriate S1 messages between the RN and the MME(S1-based handover) and X2 messages between the RN and target eNB(X2-based handover); the DeNB is explicitly aware of a UE attached tothe RN due to the S1 proxy and X2 proxy functionality.

FIGS. 6 and 7 show an intra-MME/S-GW handover procedure.

0. The UE context within the source eNB contains information regardingroaming restrictions which were provided either at connectionestablishment or at the last TA update.

1. The source eNB configures the UE measurement procedures according tothe area restriction information. Measurements provided by the sourceeNB may assist the function controlling the UE's connection mobility.

2. The UE is triggered to send measurement reports by the rules set byi.e., system information, specification, etc.

3. The source eNB makes decision based on measurement reports and radioresource management (RRM) information to hand off the UE.

4. The source eNB issues a handover request message to the target eNBpassing necessary information to prepare the HO at the target side (UEX2 signalling context reference at source eNB, UE S1 EPC signallingcontext reference, target cell identifier (ID), K_(eNB)*, RRC contextincluding the cell radio network temporary identifier (C-RNTI) of the UEin the source eNB, AS-configuration, E-RAB context and physical layer IDof the source cell+short MAC-I for possible radio link failure (RLF)recovery). UE X2/UE S1 signalling references enable the target eNB toaddress the source eNB and the EPC. The E-RAB context includes necessaryradio network layer (RNL) and transport network layer (TNL) addressinginformation, and quality of service (QoS) profiles of the E-RABs.

5. Admission Control may be performed by the target eNB dependent on thereceived E-RAB QoS information to increase the likelihood of asuccessful HO, if the resources can be granted by target eNB. The targeteNB configures the required resources according to the received E-RABQoS information and reserves a C-RNTI and optionally a RACH preamble.The AS-configuration to be used in the target cell can either bespecified independently (i.e., an “establishment”) or as a deltacompared to the AS-configuration used in the source cell (i.e., a“reconfiguration”).

6. The target eNB prepares HO with L1/L2 and sends the handover requestacknowledge to the source eNB. The handover request acknowledge messageincludes a transparent container to be sent to the UE as an RRC messageto perform the handover. The container includes a new C-RNTI, target eNBsecurity algorithm identifiers for the selected security algorithms, mayinclude a dedicated RACH preamble, and possibly some other parameters,i.e., access parameters, SIBs, etc. The handover request acknowledgemessage may also include RNL/TNL information for the forwarding tunnels,if necessary.

As soon as the source eNB receives the handover request acknowledge, oras soon as the transmission of the handover command is initiated in thedownlink, data forwarding may be initiated.

Steps 7 to 16 in FIGS. 6 and 7 provide means to avoid data loss duringHO.

7. The target eNB generates the RRC message to perform the handover,i.e., RRCConnectionReconfiguration message including themobilityControlInformation, to be sent by the source eNB towards the UE.The source eNB performs the necessary integrity protection and cipheringof the message. The UE receives the RRCConnectionReconfiguration messagewith necessary parameters (i.e. new C-RNTI, target eNB securityalgorithm identifiers, and optionally dedicated RACH preamble, targeteNB SIBs, etc.) and is commanded by the source eNB to perform the HO.The UE does not need to delay the handover execution for delivering theHARQ/ARQ responses to source eNB.

8. The source eNB sends the sequence number (SN) status transfer messageto the target eNB to convey the uplink PDCP SN receiver status and thedownlink PDCP SN transmitter status of E-RABs for which PDCP statuspreservation applies (i.e., for RLC AM). The uplink PDCP SN receiverstatus includes at least the PDCP SN of the first missing UL servicedata unit (SDU) and may include a bit map of the receive status of theout of sequence UL SDUs that the UE needs to retransmit in the targetcell, if there are any such SDUs. The downlink PDCP SN transmitterstatus indicates the next PDCP SN that the target eNB shall assign tonew SDUs, not having a PDCP SN yet. The source eNB may omit sending thismessage if none of the E-RABs of the UE shall be treated with PDCPstatus preservation.

9. After receiving the RRCConnectionReconfiguration message includingthe mobilityControlInformation, UE performs synchronization to targeteNB and accesses the target cell via RACH, following a contention-freeprocedure if a dedicated RACH preamble was indicated in themobilityControlInformation, or following a contention-based procedure ifno dedicated preamble was indicated. UE derives target eNB specific keysand configures the selected security algorithms to be used in the targetcell.

10. The target eNB responds with UL allocation and timing advance.

11. When the UE has successfully accessed the target cell, the UE sendsthe RRCConnectionReconfigurationComplete message (C-RNTI) to confirm thehandover, along with an uplink buffer status report, whenever possible,to the target eNB to indicate that the handover procedure is completedfor the UE. The target eNB verifies the C-RNTI sent in theRRCConnectionReconfigurationComplete message. The target eNB can nowbegin sending data to the UE.

12. The target eNB sends a path switch request message to MME to informthat the UE has changed cell.

13. The MME sends a modify bearer request message to the servinggateway.

14. The serving gateway switches the downlink data path to the targetside. The Serving gateway sends one or more “end marker” packets on theold path to the source eNB and then can release any U-plane/TNLresources towards the source eNB.

15. The serving gateway sends a modify bearer response message to MME.

16. The MME confirms the path switch request message with the pathswitch request acknowledge message.

17. By sending the UE context release message, the target eNB informssuccess of HO to source eNB and triggers the release of resources by thesource eNB. The target eNB sends this message after the path switchrequest acknowledge message is received from the MME.

18. Upon reception of the UE context release message, the source eNB canrelease radio and C-plane related resources associated to the UEcontext. Any ongoing data forwarding may continue.

When an X2 handover is used between home eNBs (HeNBs) and when thesource HeNB is connected to a HeNB GW, a UE context release requestmessage including an explicit GW context release indication is sent bythe source HeNB, in order to indicate that the HeNB GW may release ofall the resources related to the UE context.

U-plane handling is described. The U-plane handling during theintra-E-UTRAN-access mobility activity for UEs in EPS connectionmanagement (ECM)-CONNECTED takes the following principles into accountto avoid data loss during HO:

-   -   During HO preparation U-plane tunnels can be established between        the source eNB and the target eNB. There is one tunnel        established for uplink data forwarding and another one for        downlink data forwarding for each E-RAB for which data        forwarding is applied. In the case of a UE under an RN        performing handover, forwarding tunnels can be established        between the RN and the target eNB via the DeNB.    -   During HO execution, user data can be forwarded from the source        eNB to the target eNB. The forwarding may take place in a        service and deployment dependent and implementation specific        way.    -   Forwarding of downlink user data from the source to the target        eNB should take place in order as long as packets are received        at the source eNB from the EPC or the source eNB buffer has not        been emptied.    -   During HO completion, the target eNB sends a paths switch        message to MME to inform that the UE has gained access and MME        sends a modify bearer request message to the serving gateway,        the U-plane path is switched by the serving gateway from the        source eNB to the target eNB. The source eNB should continue        forwarding of U-plane data as long as packets are received at        the source eNB from the serving gateway or the source eNB buffer        has not been emptied.

For RLC-AM bearers, during normal HO not involving full configuration,for in-sequence delivery and duplication avoidance, PDCP SN ismaintained on a bearer basis and the source eNB informs the target eNBabout the next DL PDCP SN to allocate to a packet which does not have aPDCP sequence number yet (either from source eNB or from the servinggateway). For security synchronization, hyper frame number (HFN) is alsomaintained and the source eNB provides to the target one reference HFNfor the UL and one for the DL, i.e., HFN and corresponding SN. In boththe UE and the target eNB, a window-based mechanism is needed forduplication detection. The occurrence of duplicates over the airinterface in the target eNB is minimised by means of PDCP SN basedreporting at the target eNB by the UE. In uplink, the reporting isoptionally configured on a bearer basis by the eNB and the UE shouldfirst start by transmitting those reports when granted resources in thetarget eNB. In downlink, the eNB is free to decide when and for whichbearers a report is sent and the UE does not wait for the report toresume uplink transmission. The target eNB re-transmits and prioritizesall downlink PDCP SDUs forwarded by the source eNB (i.e., the target eNBshould send data with PDCP SNs from X2 before sending data from S1),with the exception of PDCP SDUs of which the reception was acknowledgedthrough PDCP SN based reporting by the UE. The UE re-transmits in thetarget eNB all uplink PDCP SDUs starting from the first PDCP SDUfollowing the last consecutively confirmed PDCP SDU, i.e., the oldestPDCP SDU that has not been acknowledged at RLC in the source, excludingthe PDCP SDUs of which the reception was acknowledged through PDCP SNbased reporting by the target.

For RLC-AM bearers, during HO involving full configuration, thefollowing description below for RLC-UM bearers also applies for RLC-AMbearers. Data loss may happen.

For RLC-UM bearers, the PDCP SN and HFN are reset in the target eNB. NoPDCP SDUs are retransmitted in the target eNB. The target eNBprioritizes all downlink PDCP SDUs forwarded by the source eNB if any(i.e., the target eNB should send data with PDCP SNs from X2 beforesending data from S1). The UE PDCP entity does not attempt to retransmitany PDCP SDU in the target cell for which transmission had beencompleted in the source cell. Instead UE PDCP entity starts thetransmission with other PDCP SDUs.

Path switch is described. It may be referred to Section 10.1.2.2 of 3GPPTS 36.300 V11.4.0 (2012-12).

After the downlink path is switched at the serving GW downlink packetson the forwarding path and on the new direct path may arriveinterchanged at the target eNB. The target eNB should first deliver allforwarded packets to the UE before delivering any of the packetsreceived on the new direct path. The method employed in the target eNBto enforce the correct delivery order of packets is outside the scope ofthe standard.

In order to assist the reordering function in the target eNB, theserving GW shall send one or more “end marker” packets on the old pathimmediately after switching the path for each E-RAB of the UE. The “endmarker” packet shall not contain user data. The “end marker” isindicated in the GPRS tunneling protocol (GTP) header. After completingthe sending of the tagged packets the GW shall not send any further userdata packets via the old path.

Upon receiving the “end marker” packets, the source eNB shall, ifforwarding is activated for that bearer, forward the packet toward thetarget eNB.

On detection of an “end marker” the target eNB shall discard the endmarker packet and initiate any necessary processing to maintain insequence delivery of user data forwarded over X2 interface and user datareceived from the serving GW over S1 as a result of the path switch.

On detection of the “end marker”, the target eNB may also initiate therelease of the data forwarding resource. However, the release of thedata forwarding resource is implementation dependent and could also bebased on other mechanisms (e.g., timer-based mechanism).

EPC may change the uplink end-point of the tunnels with path switchprocedure. However, the EPC should keep the old GTP tunnel end-point(s)sufficiently long time in order to minimize the probability of packetlosses and avoid unintentional release of respective E-RAB(s).

Data forwarding is described. It may be referred to Section 10.1.2.3 of3GPP TS 36.300 V11.4.0 (2012-12).

Upon handover, the source eNB may forward in order to the target eNB alldownlink PDCP SDUs with their SN that have not been acknowledged by theUE. In addition, the source eNB may also forward without a PDCP SN freshdata arriving over S1 to the target eNB. The target eNB does not have towait for the completion of forwarding from the source eNB before itbegins transmitting packets to the UE.

The source eNB discards any remaining downlink RLC PDUs.Correspondingly, the source eNB does not forward the downlink RLCcontext to the target eNB. The source eNB does not need to abort ongoing RLC transmissions with the UE as it starts data forwarding to thetarget eNB.

For RLC-AM DRBs, upon handover, the source eNB forwards to the servinggateway the uplink PDCP SDUs successfully received in-sequence until thesending of the status transfer message to the target eNB. Then at thatpoint of time the source eNB stops delivering uplink PDCP SDUs to theS-GW and shall discard any remaining uplink RLC PDUs. Correspondingly,the source eNB does not forward the uplink RLC context to the targeteNB.

Then the source eNB shall either:

-   -   discard the uplink PDCP SDUs received out of sequence if the        source eNB has not accepted the request from the target eNB for        uplink forwarding or if the target eNB has not requested uplink        forwarding for the bearer during the Handover Preparation        procedure,    -   forward to the target eNB the uplink PDCP SDUs received out of        sequence if the source eNB has accepted the request from the        target eNB for uplink forwarding for the bearer during the        Handover Preparation procedure.

The PDCP SN of forwarded SDUs is carried in the “PDCP PDU number” fieldof the GTP-U extension header. The target eNB shall use the PDCP SN ifit is available in the forwarded GTP-U packet.

For normal HO in-sequence delivery of upper layer PDUs during handoveris based on a continuous PDCP SN and is provided by the “in-orderdelivery and duplicate elimination” function at the PDCP layer:

-   -   in the downlink, the “in-order delivery and duplicate        elimination” function at the UE PDCP layer guarantees        in-sequence delivery of downlink PDCP SDUs;    -   in the uplink, the “in-order delivery and duplicate elimination”        function at the target eNB PDCP layer guarantees in-sequence        delivery of uplink PDCP SDUs.

After a normal handover, when the UE receives a PDCP SDU from the targeteNB, it can deliver it to higher layer together with all PDCP SDUs withlower SNs regardless of possible gaps.

For handovers involving full configuration, the source eNB behavior isunchanged from the description above. The target eNB may not send PDCPSDUs for which delivery was attempted by the source eNB. The target eNBidentifies these by the presence of the PDCP SN in the forwarded GTP-Upacket and discards them.

After a full configuration handover, the UE delivers received PDCP SDUfrom the source cell to the higher layer regardless of possible gaps. UEdiscards uplink PDCP SDUs for which transmission was attempted andretransmission of these over the target cell is not possible.

For RLC-UM DRBs, upon handover, the source eNB does not forward to thetarget eNB downlink PDCP SDUs for which transmission had been completedin the source cell. PDCP SDUs that have not been transmitted may beforwarded. In addition, the source eNB may forward fresh downlink dataarriving over S1 to the target eNB. The source eNB discards anyremaining downlink RLC PDUs. Correspondingly, the source eNB does notforward the downlink RLC context to the target eNB.

Upon handover, the source eNB forwards all uplink PDCP SDUs successfullyreceived to the serving gateway (i.e., including the ones received outof sequence) and discards any remaining uplink RLC PDUs.Correspondingly, the source eNB does not forward the uplink RLC contextto the target eNB.

With respect to SRBs, the following principles apply at HO:

-   -   No forwarding or retransmissions of RRC messages in the target;    -   The PDCP SN and HFN are reset in the target.

Carrier aggregation (CA) is described. It may be referred to Section 5.5of 3GPP TS 36.300 V11.4.0 (2012-12).

CA is supported for both contiguous and non-contiguous CCs with each CClimited to a maximum of 110 resource blocks in the frequency domainusing the Rel-8/9 numerology.

It is possible to configure a UE to aggregate a different number of CCsoriginating from the same eNB and of possibly different bandwidths inthe UL and the DL.

-   -   The number of DL CCs that can be configured depends on the DL        aggregation capability of the UE;    -   The number of UL CCs that can be configured depends on the UL        aggregation capability of the UE;    -   It is not possible to configure a UE with more UL CCs than DL        CCs;    -   In typical TDD deployments, the number of CCs and the bandwidth        of each CC in UL and DL is the same.

CCs originating from the same eNB need not to provide the same coverage.

CCs shall be LTE Rel-8/9 compatible. Nevertheless, existing mechanisms(e.g., barring) may be used to avoid Rel-8/9 UEs to camp on a CC.

The spacing between center frequencies of contiguously aggregated CCsshall be a multiple of 300 kHz. This is in order to be compatible withthe 100 kHz frequency raster of Rel-8/9 and at the same time preserveorthogonality of the subcarriers with 15 kHz spacing. Depending on theaggregation scenario, the n×300 kHz spacing can be facilitated byinsertion of a low number of unused subcarriers between contiguous CCs.

The configured set of serving cells for a UE therefore always consistsof one PCell and one or more SCells:

-   -   For each SCell the usage of uplink resources by the UE in        addition to the downlink ones is configurable (the number of DL        SCCs configured is therefore always larger than or equal to the        number of UL SCCs and no SCell can be configured for usage of        uplink resources only);    -   From a UE viewpoint, each uplink resource only belongs to one        serving cell;    -   The number of serving cells that can be configured depends on        the aggregation capability of the UE;    -   PCell can only be changed with handover procedure (i.e., with        security key change and RACH procedure);    -   PCell is used for transmission of PUCCH;    -   Unlike SCells, PCell cannot be de-activated;    -   Re-establishment is triggered when PCell experiences RLF, not        when SCells experience RLF;    -   NAS information is taken from PCell.

The reconfiguration, addition and removal of SCells can be performed byRRC. At intra-LTE handover, RRC can also add, remove, or reconfigureSCells for usage with the target PCell. When adding a new SCell,dedicated RRC signaling is used for sending all required systeminformation of the SCell, i.e., while in connected mode, UEs need notacquire broadcasted system information directly from the SCells.

SCell addition/modification is described. It may be referred to Section5.3.10.3b of 3GPP TS 36.331 V11.1.0 (2012-09). The UE shall:

1> for each sCellIndex value included in the sCellToAddModList that isnot part of the current UE configuration (SCell addition):

2> add the SCell, corresponding to the cellIdentification, in accordancewith the received radioResourceConfigCommonSCell andradioResourceConfigDedicatedSCell;

2> configure lower layers to consider the SCell to be in deactivatedstate;

1> for each sCellIndex value included in the sCellToAddModList that ispart of the current UE configuration (SCell modification):

2> modify the SCell configuration in accordance with the receivedradioResourceConfigDedicatedSCell.

SCell release is described. It may be referred to Section 5.3.10.3a of3GPP TS 36.331 V11.1.0 (2012-09). The UE shall:

1> if the release is triggered by reception of the sCellToReleaseList:

2> for each sCellIndex value included in the sCellToReleaseList:

3> if the current UE configuration includes an SCell with valuesCellIndex:

4> release the SCell;

1> if the release is triggered by RRC connection re-establishment:

2> release all SCells that are part of the current UE configuration.

Dual connectivity for small cell enhancement has been studied. Dualconnectivity may imply:

-   -   Control and data separation where, for instance, the control        signaling for mobility is provided via the macro layer at the        same time as high-speed data connectivity is provided via the        low-power layer.    -   A separation between downlink and uplink, where downlink and        uplink connectivity is provided via different layers.    -   Diversity for control signaling, where radio resource control        (RRC) signaling may be provided via multiple links, further        enhancing mobility performance.

FIG. 8 shows a scenario of dual connectivity.

Referring to FIG. 8, the UE has an RRC connection with the master eNB(hereinafter, MeNB). In dual connectivity, the MeNB controls the macrocell, and is the eNB which terminates at least S1-MME and therefore actas mobility anchor towards the CN. Also, the UE has a radio link withthe secondary eNB (hereinafter, SeNB). In dual connectivity, the SeNBcontrols one or more small cells, and is the eNB providing additionalradio resources for the UE, which is not the MeNB. Accordingly, the UEmay receive control signaling from the MeNB, and may receive data fromthe SeNB. The MeNB and SeNB has a network interface between thereof, andtherefore, information may be exchanged between the MeNB and SeNB.

According to the prior art, when the UE reports measurement resultsabout one or more cells on one or more frequencies to the eNB, the eNBcould send RRC connection reconfiguration to the UE in order toconfigure one or more SCells. Upon receiving the RRC connectionreconfiguration including SCell configurations, the UE configures one ormore SCells. Hence, the UE configures SCell under the network's control.However, if the UE moves fast, the network controlled SCellconfiguration is not efficient, because adding and releasing SCell wouldoccur frequently.

Therefore, UE-based SCell configuration may be proposed according to anembodiment of the present invention. According to an embodiment of thepresent invention, the UE configures a condition of adding or releasingan SCell (with a list of potential SCells), and measures one or morecells. If an SCell meets the condition of adding an SCell (and if theSCell is included in the list of potential SCells), the UE adds a SCell,and indicates the added SCell to the eNB. Alternatively, if the SCellhas been configured before and if the SCell meets the condition ofreleasing a SCell, the UE releases the SCell.

The UE may select a value of a SCell index for the added SCell (amongSCell indices not allocated to any other SCell before), and may indicatethe selected value of the SCellIndex to the eNB. The condition of addinga SCell may be A6-1 event, which will be described later. The conditionof releasing a SCell may be A6-2 event, which will be described later.Further, the UE may deactivates or release a SCell which has beenpreviously configured on the frequency where the added SCell is located.Further, the UE may deactivate the added SCell when the SCell is added.In the description above, PCell and SCell may or may not belong todifferent eNBs via X2 interface.

FIG. 9 shows a UE-based SCell addition procedure according to anembodiment of the present invention.

In step S100, if the SCell and the PCell belong to different eNBs, theeNB controlling the SCell may provide information about the SCell toneighboring eNB controlling the PCell.

In step S110, the PCell is able to inform UE about information relatedto one or more SCells that UE could potentially configure. Theinformation may be signaled to the UE via an RRC connectionreconfiguration message on a DCCH or system information on a BCCH. Theinformation may contain a list of SCells, SCell configuration and SCelladdition/release condition. Information about the list of SCells maycontain a cell ID and a carrier frequency of each listed SCell. TheSCell configuration may correspond to default SCell configurationapplied to the list of SCells. The SCell addition/release condition maybe provided either for each frequency where one of the listed SCells isplaced or for all frequencies where the listed SCells are placed.

In step S120, the UE performs measurement on one or more frequencieswhere the listed SCells are placed in order to find a listed SCell.

In step S130, if the UE detects a listed SCell, the UE verifies whetheror not the detected SCell satisfies the SCell addition condition. TheSCell addition condition may be A6-1 event, which is defined by Equation1 below.

Mn+Ofn+Ocn−Hys>Mp+Ofp+Ocp+Off  <Equation 1>

Mn is the measurement result of the detected listed SCell, not takinginto account any offsets.

Ofn is the frequency specific offset of the frequency of the detectedlisted SCell (i.e., offsetFreq as defined within measObjectEUTRAcorresponding to the frequency of the detected listed SCell).

Ocn is the cell specific offset of the detected listed SCell (i.e.,cellIndividualOffset as defined within measObjectEUTRA corresponding tothe frequency of the detected listed SCell), and set to zero if notconfigured for the detected listed SCell.

Hys is the hysteresis parameter for this event (i.e., hysteresis asdefined within reportConfigEUTRA for this event).

Mp is the measurement result of either the PCell or the SCell that iscurrently configured on the frequency of the detected listed SCell, nottaking into account any offsets.

Ofp is the frequency specific offset of either the frequency of thePCell or the frequency of the SCell that is currently configured on thefrequency of the detected listed SCell (i.e., offsetFreq as definedwithin measObjectEUTRA corresponding to the corresponding frequency).

Ocp is the cell specific offset of either the PCell or the SCell that iscurrently configured on the frequency of the detected listed SCell(i.e., cellIndividualOffset as defined within measObjectEUTRAcorresponding to the corresponding frequency), and is set to zero if notconfigured for the PCell or the SCell.

Off is the offset parameter for this event (i.e., a3-Offset as definedwithin reportConfigEUTRA for this event).

Mn, Mp are expressed in dBm in case of reference signal received power(RSRP), or in dB in case of reference signal received quality (RSRQ).Ofn, Ocn, Ofp, Ocp, Hys, Off are expressed in dB.

In step S140, if the detected cell is included in the list of SCells,and if the detected cell satisfies the SCell addition condition, e.g.,for a certain time duration which is configured in step S110 above, theUE adds the cell as a new SCell with the SCell configuration. The UEconsiders the added SCell as deactivated. If a certain SCell has beenpreviously configured on the frequency of the added SCell before, UE mayrelease the previously configured SCell upon adding the new SCell.

In step S150, upon adding the new SCell, the UE selects one of SCellindices not assigned to any other configured SCell, and then assigns theselected SCell index to the new SCell. And, upon adding the new SCell,the UE informs the eNB about the new SCell information via a small cellindication message. The informed eNB can be either the eNB controllingthe PCell or the eNB controlling the SCell. The new SCell informationincludes the SCell index assigned to the new SCell, the frequency of theSCell, and the cell ID of the SCell.

If the new SCell information is signaled to the eNB controlling thePCell, and if the eNB controlling the PCell is different than the eNBcontrolling the SCell, in step S160, the eNB controlling the PCell maytransmit the received new SCell information to the eNB controlling theSCell with the UE identity. In step S170, the eNB controlling the SCellmay or may not accept this SCell addition by transmitting an SCelladdition response to the eNB controlling the PCell.

After receiving the small cell indication adding the new SCell, in stepS180, the eNB controlling the PCell may transmit an RRC connectionreconfiguration message in order to indicate to the UE that the additionof the new SCell is accepted or rejected, or in order to reconfigure thenew SCell for the UE.

If the addition of the new SCell is accepted, the UE keeps the new Scelland may activate the new SCell. If the addition of the new SCell is notaccepted but rejected, the UE may release or deactivate the new SCell.If the new SCell is reconfigured, the UE reconfigures the new SCell byusing information included in the RRC connection reconfigurationmessage.

In step S190, the eNB controlling the PCell activates the new SCell bytransmitting an activation/deactivation MAC control element (CE)indicating activation of the SCell index assigned to the new SCell. Uponreceiving the activation/deactivation MAC CE indicating activation ofthe SCell index assigned to the new SCell, the UE activates the newSCell.

FIG. 10 shows a UE-based SCell release procedure according to anembodiment of the present invention.

In step S200, the PCell is able to inform UE about information relatedto one or more SCells that UE could potentially configure. Theinformation may be signaled to the UE via an RRC connectionreconfiguration message on a DCCH or system information on a BCCH. Theinformation may contain a list of SCells, SCell configuration and SCelladdition/release condition. Information about the list of SCells maycontain a cell ID and a carrier frequency of each listed SCell. TheSCell configuration may correspond to default SCell configurationapplied to the list of SCells. The SCell addition/release condition maybe provided either for each frequency where one of the listed SCells isplaced or for all frequencies where the listed SCells are placed.

In step S210, the UE performs measurement on one or more configuredSCells.

In step S220, the UE identifies the cell that satisfies the SCellrelease condition.

The SCell release condition may be A6-2 event, which is defined byEquation 2 below.

Mn+Ofn+Ocn−Hys<Mp+Ofp+Ocp+Off  <Equation 2>

Mn is the measurement result of the detected listed SCell, not takinginto account any offsets.

Ofn is the frequency specific offset of the frequency of the detectedlisted SCell (i.e., offsetFreq as defined within measObjectEUTRAcorresponding to the frequency of the detected listed SCell).

Ocn is the cell specific offset of the detected listed SCell (i.e.,cellIndividualOffset as defined within measObjectEUTRA corresponding tothe frequency of the detected listed SCell), and set to zero if notconfigured for the detected listed SCell.

Hys is the hysteresis parameter for this event (i.e., hysteresis asdefined within reportConfigEUTRA for this event).

Mp is the measurement result of either the PCell or the SCell that iscurrently configured on the frequency of the detected listed SCell, nottaking into account any offsets.

Ofp is the frequency specific offset of either the frequency of thePCell or the frequency of the SCell that is currently configured on thefrequency of the detected listed SCell (i.e., offsetFreq as definedwithin measObjectEUTRA corresponding to the corresponding frequency).

Ocp is the cell specific offset of either the PCell or the SCell that iscurrently configured on the frequency of the detected listed SCell(i.e., cellIndividualOffset as defined within measObjectEUTRAcorresponding to the corresponding frequency), and is set to zero if notconfigured for the PCell or the SCell.

Off is the offset parameter for this event (i.e., a3-Offset as definedwithin reportConfigEUTRA for this event).

Mn, Mp are expressed in dBm in case of reference signal received power(RSRP), or in dB in case of reference signal received quality (RSRQ).Ofn, Ocn, Ofp, Ocp, Hys, Off are expressed in dB.

If the configured SCell satisfies the SCell release condition, e.g., fora certain time duration which is configured in step S200, in step S230,the UE deactivates or releases the cell with the SCell configuration.

Upon deactivating or releasing the SCell, in step S240, the UE indicatesto the eNB that the SCell is deactivated or released via a small cellindication message. The small cell indication message may include thereleased SCell information and SCell index of the released SCell.Alternatively, in step S250, the eNB controlling the PCell may indicatedeactivation of the SCell to the UE by transmitting anactivation/deactivation MAC CE indicating deactivation of the SCell.

After receiving the small cell indication, in step S260, the eNBcontrolling the PCell may transmit an RRC connection reconfigurationmessage in order to release the SCell for the UE, or in order toindicate to the UE that the release of the new SCell is accepted orrejected.

If the release of the SCell is accepted, the UE releases the SCell. Ifthe release of the new SCell is not accepted but rejected, the UE maykeep the SCell and consider the SCell as deactivated. If the new SCellis released, the UE releases the SCell according to the RRC connectionreconfiguration message.

If the SCell is released, and if the eNB controlling the PCell isdifferent than the eNB controlling the SCell, in step S270, the eNBcontrolling the PCell may inform the eNB controlling the SCell aboutrelease of the SCell with the UE identity and released SCellinformation. In step S280, the eNB controlling the SCell may or may notaccept this SCell release by transmitting an SCell release response tothe eNB controlling the PCell.

FIG. 11 shows an example of a method for transmitting informationaccording to an embodiment of the present invention.

In step S300, the first node receives an indication which indicates thata SCell is added by the UE, and information on the added SCell. Theinformation on the added SCell may include at least one of an index ofthe added SCell, a frequency of the added SCell, and a cell ID of theadded SCell. The index of the added SCell may be an index not assignedto other configured SCell. The indication and the information on theadded SCell may be received via a small cell indication message.

In step S310, the first node transmits an SCell addition request,including the information on the added SCell and an identity of the UE,to a second node. The first node may be the MeNB controlling the PCell,and the second node is the SeNB controlling the SCell. The first nodeand the second node may be different from each other. The second nodemay transmit an SCell addition response to the first node as a responseto the SCell addition request.

FIG. 12 shows an example of a method for transmitting informationaccording to another embodiment of the present invention.

In step S400, the first node receives an indication which indicates thata SCell is released by the UE, and information on the released SCell.The information on the released SCell may include an index of thereleased SCell. The indication and the information on the released SCellmay be received via a small cell indication message.

In step S410, the first node transmits an SCell release request,including the information on the released SCell and an identity of theUE, to a second node. The first node may be the MeNB controlling thePCell, and the second node is the SeNB controlling the SCell. The firstnode and the second node may be different from each other. The secondnode may transmit an SCell release response to the first node as aresponse to the SCell release request.

FIG. 13 is a block diagram showing wireless communication system toimplement an embodiment of the present invention.

An eNB 800 may include a processor 810, a memory 820 and a radiofrequency (RF) unit 830. The processor 810 may be configured toimplement proposed functions, procedures and/or methods described inthis description. Layers of the radio interface protocol may beimplemented in the processor 810. The memory 820 is operatively coupledwith the processor 810 and stores a variety of information to operatethe processor 810. The RF unit 830 is operatively coupled with theprocessor 810, and transmits and/or receives a radio signal.

A UE 900 may include a processor 910, a memory 920 and a RF unit 930.The processor 910 may be configured to implement proposed functions,procedures and/or methods described in this description. Layers of theradio interface protocol may be implemented in the processor 910. Thememory 920 is operatively coupled with the processor 910 and stores avariety of information to operate the processor 910. The RF unit 930 isoperatively coupled with the processor 910, and transmits and/orreceives a radio signal.

The processors 810, 910 may include application-specific integratedcircuit (ASIC), other chipset, logic circuit and/or data processingdevice. The memories 820, 920 may include read-only memory (ROM), randomaccess memory (RAM), flash memory, memory card, storage medium and/orother storage device. The RF units 830, 930 may include basebandcircuitry to process radio frequency signals. When the embodiments areimplemented in software, the techniques described herein can beimplemented with modules (e.g., procedures, functions, and so on) thatperform the functions described herein. The modules can be stored inmemories 820, 920 and executed by processors 810, 910. The memories 820,920 can be implemented within the processors 810, 910 or external to theprocessors 810, 910 in which case those can be communicatively coupledto the processors 810, 910 via various means as is known in the art.

In view of the exemplary systems described herein, methodologies thatmay be implemented in accordance with the disclosed subject matter havebeen described with reference to several flow diagrams. While forpurposed of simplicity, the methodologies are shown and described as aseries of steps or blocks, it is to be understood and appreciated thatthe claimed subject matter is not limited by the order of the steps orblocks, as some steps may occur in different orders or concurrently withother steps from what is depicted and described herein. Moreover, oneskilled in the art would understand that the steps illustrated in theflow diagram are not exclusive and other steps may be included or one ormore of the steps in the example flow diagram may be deleted withoutaffecting the scope and spirit of the present disclosure.

What is claimed is:
 1. A method for transmitting, by a first node,information in a wireless communication system, the method comprising:receiving an indication which indicates that a secondary cell (SCell) isadded by a user equipment (UE), and information on the added SCell; andtransmitting an SCell addition request, including the information on theadded SCell and an identity of the UE, to a second node.
 2. The methodof claim 1, wherein the information on the added SCell includes at leastone of an index of the added SCell, a frequency of the added SCell, anda cell identifier (ID) of the added SCell.
 3. The method of claim 2,wherein the index of the added SCell is an index not assigned to otherconfigured SCell.
 4. The method of claim 1, wherein the indication andthe information on the added SCell are received via a small cellindication message.
 5. The method of claim 1, wherein the first node isa master eNodeB (MeNB) controlling a primary cell (PCell), and whereinthe second node is a secondary eNodeB (SeNB) controlling the SCell. 6.The method of claim 1, wherein the first node and the second node isdifferent from each other.
 7. The method of claim 1, further comprising:receiving an SCell addition response from the second node as a responseto the SCell addition request.
 8. A method for transmitting, by a firstnode, information in a wireless communication system, the methodcomprising: receiving an indication which indicates that a secondarycell (SCell) is released by a user equipment (UE), and information onthe released SCell; and transmitting an SCell release request, includingthe information on the released SCell and an identity of the UE, to asecond node.
 9. The method of claim 8, wherein the information on thereleased SCell includes an index of the released SCell.
 10. The methodof claim 8, wherein the indication and the information on the releasedSCell are received via a small cell indication message.
 11. The methodof claim 8, wherein the first node is a master eNodeB (MeNB) controllinga primary cell (PCell), and wherein the second node is a secondaryeNodeB (SeNB) controlling the SCell.
 12. The method of claim 8, whereinthe first node and the second node is different from each other.
 13. Themethod of claim 8, further comprising: receiving an SCell releaseresponse from the second node as a response to the SCell releaserequest.
 14. A method for adding, by a user equipment (UE), a secondarycell (SCell) in a wireless communication system, the method comprising:receiving a list of potential SCells, an SCell configuration, and acondition of SCell addition; measuring one or more SCells; adding anSCell if the SCell meets the condition of SCell addition and if theSCell is included in the list of potential SCells; and transmitting anindex of the added SCell to an eNodeB (eNB).
 15. The method of claim 14,wherein the index of the added SCell is an index not assigned to otherconfigured SCells.